JavaScript arrays declaration ways difference - javascript

This could be a pretty basic question, in JavaScript, what's difference between:
var userDetails = {};
var usersList = [];
I was reading an article which had following code:
function GetSampleUsersList() {
var userDetails = {};
var usersList = [];
for (var i = 1; i <= 3; i++) {
userDetails["UserId"] = i;
userDetails["UserName"] = "User- " + i;
userDetails["Company"] = "Company- " + i;
usersList.push(userDetails);
}
return JSON.stringify(usersList);
}
Thanks


This is a pretty basic question.
var o = {}
initializes an empty object. Then you assign its properties.
var a = []
initializes an empty array. You then add the newly created object to the array
a.push( o );


You are using for every iteration the same userDetails, because you overwrite just the properties and while you have pushed the same object, you have always the same content for every element in the array.
function GetSampleUsersList() {
var userDetails = {};
var usersList = [];
for (var i = 1; i <= 3; i++) {
userDetails["UserId"] = i;
userDetails["UserName"] = "User- " + i;
userDetails["Company"] = "Company- " + i;
usersList.push(userDetails);
}
return JSON.stringify(usersList);
}
console.log(GetSampleUsersList());
Better use a new empty object for every loop.
function GetSampleUsersList() {
var userDetails;
var usersList = [];
for (var i = 1; i <= 3; i++) {
userDetails = {}; // this is necessary
userDetails["UserId"] = i;
userDetails["UserName"] = "User- " + i;
userDetails["Company"] = "Company- " + i;
usersList.push(userDetails);
}
return JSON.stringify(usersList);
}
console.log(GetSampleUsersList());


function GetSampleUsersList() {
var userDetails = {}; //created an empty object userDetails
var usersList = []; //created an empty array userDetails
for (var i = 1; i <= 3; i++) { //looping to add property and value in object and for each iteration object is getting pushed into array at an index i.
userDetails["UserId"] = i;
userDetails["UserName"] = "User- " + i;
userDetails["Company"] = "Company- " + i;
usersList.push(userDetails); // pushing object {"UserId":i, "UserName":"User-i", "Company":"Company-i"} into array
}
return JSON.stringify(usersList); // Parsing the object into javascript string
}


var userDetails = {}; -- object notation in javascript
var usersList = []; is an array notation in javascript.
for more infomation refer here http://yuiblog.com/blog/2006/11/13/javascript-we-hardly-new-ya/

Related

Access the array Object property value through for loop

I want access the object property which in inside array how to access that through a for loop ex:
arr[{A:1},{A:2},{B:3},{C:3}]
i want sum of each object.

let arr = [{A:1},{A:2},{B:3},{C:3}]
let sum = arr.reduce((ac, o) => ac + Object.values(o)[0], 0);
console.log(sum);

If you have same known key in object, then you can try this
var data = [{a:6},{a:8},{a:9}];
var dataLength = data.length;
var total = 0;
var i = 0;
while(i < dataLength){
total += data[i]["a"];
i++;
}
If you have object with unkown keys / dynamic keys, then use this,
var data = [{a:6},{b:8},{c:9,e:5}];
var dataLength = data.length;
var total = 0;
var i = 0;
while(i < dataLength){
for(var propName in data) {
if(data.hasOwnProperty(propName)) {
var propValue = data[propName];
total += propValue;
}
}
i++;
}

Defining a 3D array in JavaScript

I tried to define a 3D array on Google Sheet, but even though I'm using the .slice() method it keeps passing the array by reference.
var temp = [];
for (var a = 0; a<archetypesAll.length; a++) {temp[a] = [0, a].slice();};
var archRank = [];
for (var a = 0; a<21; a++) {archRank[a]= temp.slice();};
archRank[2][1][0] = 'Test';
I want to edit a single element of the matrix but instead the code above just fills every row with the exact same value ('Test'):
3DMatrix[x][1][0] = 'Test'

You can't just copy a multidimensional array by calling slice at the top level, because that will not deep-copy the whole. You have to write your own deepCopy methid, like this:
function allocate(mainDim, ...dims) {
const result = new Array(mainDim);
for (let i = 0; i < result.length; i++) {
result[i] = dims.length > 0 ? allocate(...dims) : 0;
}
return result;
}
function deepCopy(matrix, dims) {
return dims > 1 ? matrix.map(row => deepCopy(row, dims - 1)) : matrix.slice();
}
function test() {
const mx1 = allocate(3,2,2);
mx1[2][1][0] = "Test";
console.log(JSON.stringify(mx1));
const mx2 = deepCopy(mx1, 3);
mx2[2][1][0] = "Copied";
console.log(JSON.stringify(mx1));
console.log(JSON.stringify(mx2));
}
test();

var array = ["Test", "Test"];
var array3d = [[array.slice(0)],[[array.slice(0)]]];
array3d[0][0][0] = "Changed";
console.log(JSON.stringify(array3d)); //[[["Changed","Test"]],[[["Test","Test"]]]]
Try with this instead of slice to get a new array instead of reference:
var temp = [];
for (var a = 0; a < archetypesAll.length; a++) {
temp[a] = JSON.parse(JSON.stringify([0, a]));
}
var archRank = [];
for (var a = 0; a < 21; a++) {
archRank[a]= temp.slice();
}
archRank[2][1][0] = 'Test';

Javascript, consolidate array elements

I'm stuck of finding a way to consolidate array elements.
so my array is in format of [id1:port1,id2:port2,id1:port3,id2:port4,id5:port5...] where each element has 2 portions. The id portion is not unique. what I try to consolidate is to create a new array will have data like [id1#port1:port3,id2#port2:port4,id5#port5]
I tried code below but it didn't get me too far. can any guru help me out?
var orinString = "id1:port1,id2:port2,id1:port3,id2:port4,id5:port5";
var newArray1 = orinString.split(",");
var newArray2 = orinString.split(",");
var newArray3 = [];
for (x=0; x<=newArray1.length-1; x++) {
for (y=0; y<= newArray2.length-1; y++) {
if ((newArray1[x].split(":")[0] == newArray2[y].split(":")[0]) && (newArray1[x].split(":")[1] != newArray2[y].split(":")[1])) {
newArray3.push(newArray1[x].split(":")[0] +"#"+ newArray1[x].split(":")[1]);
}
}
}
for (z=0; z<=newArray3.length; z++) {
gs.log("show me the result " +newArray3[z]);
}

is it that you want:
var orinString = "id1:port1,id2:port2,id1:port3,id2:port4,id5:port5";
var arr1 = orinString.split(",");
var temp= "";
var newStr = "";
arr1.sort();
for(i=0; i< arr1.length; i++) {
var item = arr1[i].split(':');
if(item[0] !== temp || temp === "") {
newStr += "," + item[0] + "#" + item[1];
} else {
newStr += ":"+item[1];
}
temp = item[0];
}
console.log(newStr.substring(1));

A typical way to solve a problem like this is
Convert them into workable values
Populate some kind of lookup table
Output the results of this lookup table
For example
var orinString = "id1:port1,id2:port2,id1:port3,id2:port4,id5:port5";
var idsAndPorts = orinString.split(",");
// Populate a key lookup
var hashTable = {};
idsAndPorts.forEach(function(s) {
var splitValue = s.split(':');
var key = splitValue[0];
var value = splitValue[1];
if(hashTable[key]) {
hashTable[key].push(value);
} else {
hashTable[key] = [value];
}
});
// Now convert it back into an array again
var finalArray = [];
for(var k in hashTable) {
finalArray.push(k + '#' + hashTable[k].join(','));
}
// View the results
finalArray.forEach(function(f) {
console.log(f);
})
This does not guarantee the final array will be sorted, but you can sort it yourself if you wish.

how can I parse json with multiple lines

I have the following JSON:
[{"returnCode":"0","errorMessage":"success","Code":{},"phoneNumber":"400557704","mobile":"400089151"},
{"returnCode":"0","errorMessage":"success","Code":{},"phoneNumber":"400557705","mobile":"400089151"},
{"returnCode":"0","errorMessage":"success","Code":{},"phoneNumber":"400557706","mobile":"400089151"},
{"returnCode":"0","errorMessage":"success","Code":{},"phoneNumber":"400557707","mobile":"400089151"}]
I need to extract all "phoneNumber" using a js function.
I'm testing from using html and my function is not so good:
function getNumbers(strJSON)
{
strJSON = "[{\"errorMessage\":\"success\",\"mobile\":\"400089151\",\"phoneNumber\":\"400557704\",\"returnCode\":\"0\"},{\"errorMessage\":\"success\",\"mobile\":\"400089151\",\"phoneNumber\":\"400557705\",\"returnCode\":\"0\"},{\"errorMessage\":\"success\",\"mobile\":\"400089151\",\"phoneNumber\":\"400557706\",\"returnCode\":\"0\"}]";
var len = strJSON.length;
var begin_index = strJSON.indexOf("returnCode") - 2;
var last_index = len - 1;
var string_toSplit = strJSON.substring(begin_index, last_index);
var string_splitted = string_toSplit.split("{");
var out="";
alert(strJSON);
alert("string_splitted");
alert(string_splitted);
for ( var i = 0; i < string_splitted.length; i++)
{
if (string_splitted[i].charAt(string_splitted[i].length - 1) === ",")
{
string_splitted[i] = string_splitted[i].slice(0, -1);
}
var json = "{" + string_splitted[i];
var obj = JSON.parse(json);
if (i == string_splitted.length)
{
out = out + obj.phoneNumber;
}
else
{
out = out + obj.phoneNumber + ",";
}
}
return out;
}

For modern browsers you can use the .map() method
var j = [{"returnCode":"0","errorMessage":"success","Code":{},"phoneNumber":"400557704","mobile":"400089151"},
{"returnCode":"0","errorMessage":"success","Code":{},"phoneNumber":"400557705","mobile":"400089151"},
{"returnCode":"0","errorMessage":"success","Code":{},"phoneNumber":"400557706","mobile":"400089151"},
{"returnCode":"0","errorMessage":"success","Code":{},"phoneNumber":"400557707","mobile":"400089151"}];
var phones = j.map(function(item){return item.phoneNumber});
Update
After seeing your code (do not try to manually split/parse the json string.. use the JSON.parse method) you should use
function getNumbers(strJSON)
{
var myJson = JSON.parse( strJSON );
return myJson.map(function( item ){ return item.phoneNumber}).join(',');
}

Update: An even better way:
function getNumbers(strJSON)
{
var obj = JSON.parse(strJSON);
return obj.map(x => x.phoneNumber).join(", ")
}
Original Post:
A straight forward method is to just iterate over every object in the array and take the values out individually.
var info = [{"returnCode":"0","errorMessage":"success","Code":{},"phoneNumber":"400557704","mobile":"400089151"},
{"returnCode":"0","errorMessage":"success","Code":{},"phoneNumber":"400557705","mobile":"400089151"},
{"returnCode":"0","errorMessage":"success","Code":{},"phoneNumber":"400557706","mobile":"400089151"},
{"returnCode":"0","errorMessage":"success","Code":{},"phoneNumber":"400557707","mobile":"400089151"}];
var phoneNumbers = [];
for (var i = 0; i < info.length; i++)
{
phoneNumbers.push(info[i].phoneNumber);
}
console.log(phoneNumbers);
http://jsfiddle.net/hX69r/
UPDATE:
http://jsfiddle.net/hX69r/1/
var info = [{"returnCode":"0","errorMessage":"success","Code":{},"phoneNumber":"400557704","mobile":"400089151"},
{"returnCode":"0","errorMessage":"success","Code":{},"phoneNumber":"400557705","mobile":"400089151"},
{"returnCode":"0","errorMessage":"success","Code":{},"phoneNumber":"400557706","mobile":"400089151"},
{"returnCode":"0","errorMessage":"success","Code":{},"phoneNumber":"400557707","mobile":"400089151"}];
var infoString = JSON.stringify(info); //this just turns the object array 'info' into a string
var numbers = getNumbers(infoString);
console.log(numbers);
function getNumbers(strJSON)
{
var obj = JSON.parse(strJSON);
var phoneNumbers = [];
for (var i = 0; i < obj.length; i++)
{
phoneNumbers.push(obj[i].phoneNumber);
}
return phoneNumbers.join(", ");
}
Additional Update:
var info = [{"returnCode":"0","errorMessage":"success","Code":{},"phoneNumber":"400557704","mobile":"400089151"},
{"returnCode":"0","errorMessage":"success","Code":{},"phoneNumber":"400557705","mobile":"400089151"},
{"returnCode":"0","errorMessage":"success","Code":{},"phoneNumber":"400557706","mobile":"400089151"},
{"returnCode":"0","errorMessage":"success","Code":{},"phoneNumber":"400557707","mobile":"400089151"}];
var infoSingle = {"returnCode":"0","errorMessage":"success","Code":{},"phoneNumber":"400557704","mobile":"400089151"};
console.log(info.length); // prints 4; so you know it has the []
console.log(infoSingle.length); // prints undefined; so you know it doesn't have []

Do not try to re-invent the wheel.
There are many ways to parse JSON already:
Use JSON.parse.
Use jQuery.parseJSON

How to create a dynamic object in a loop?

Basically I want to create one large object of many object in JavaScript. Something like:
var objects = {}
for (x)
objects.x = {name: etc}
Any ideas?

var objects = {};
for (var x = 0; x < 100; x++) {
objects[x] = {name: etc};
}

An actual implementation
Populate a container object with 100 other objects.
<script>
var container = { }; // main object
// add 100 sub-object values
for(i = 0; i < 100; ++i) {
container['prop'+i ] /*property name or key of choice*/
= { 'a':'something',
'b':'somethingelse',
'c': 2 * i
};
}
TEST THE Results - iterate and display objects...
for(var p in container) {
var innerObj = container[p];
document.write('<div>container.' + p + ':' + innerObj + '</div>');
// write out properties of inner object
document.write('<div> .a: ' + innerObj['a'] + '</div>');
document.write('<div> .b: ' + innerObj['b'] + '</div>');
document.write('<div> .c: ' + innerObj['c'] + '</div>');
}
</script>
Output is like
container.prop0:[object Object]
.a: something
.b: somethingelse
.c: 0
container.prop1:[object Object]
.a: something
.b: somethingelse
.c: 2
container.prop2:[object Object]
.a: something
.b: somethingelse
.c: 4
etc...

Using object[propertyname] is the same as using object.propertyname and hence we can dynamically create object keys with object[propertyname] format
for eg:
var fruits = ["Apple", "Orange", "Banana","Grapes"];
var colors = ["red", "Orange", "yellow","blue"];
var newObj = {};
for (var i = 0; i < fruits.length; i++) {
newObj[fruits[i]] = colors[i];
}
console.log(newObj);

Try this
var objects = new Array();
var howmany = 10;
for (var i = 0; i < howmany; i++)
{
objects[i] = new Object();
}

//On Nested Obj like that
var playersCount = {
"Players" : {}
}
var exempleCount = 5;
for(i=0; i <= exempleCount;i++){
var BadID = Math.floor(Math.random() * 10000);
playersCount.Players["Player_"+i] = {
"id":BadID,
"xPos":0,
"yPos":0,
"zPos":0
};
}
console.log(playersCount);

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